1. Field of the Invention
The present invention relates to a method of memorizing travel locus data for use in an on-board navigation system for motor vehicles.
2. Description of Background Information
Recently, application of electronics in the vehicle has progressed largely, and computerized controls are now implemented in various parts of a motor vehicle such as the engine, brake, and suspension. Furthermore, navigation systems to be mounted in a vehicle for guiding the vehicle to a certain destination have entered a stage of practical application. These on-board navigation systems are constructed such that numerical data of a map is previously stored in a memory, map data of a region covering a given area including the present location of the vehicle is read out from the memory while the present location of the vehicle is being recognized, so that a map around the location of the vehicle is displayed on a display, and the location of the vehicle itself is automatically indicated in the map being displayed.
It is extremely advantageous if the travel locus is memorized by any method when the vehicle is traveling with this on-board navigation system, because it can be of great assistance when the same route is taken next time. As an example of such method, it is generally conceivable to record the travel locus every travel of predetermined distance in the form of longitude and latitude data or corresponding data of (X,Y) coordinate every time the traveling distance of vehicle reaches a particular value. With this method, however, the volume of data becomes very large especially when the vehicle travels through a long distance, thus it becomes impossible to record all of the travel locus data. It is also conceivable to thin-out the travel locus data, so as to cut down the amount of data. However, this means that accurate travel locus data cannot be held with such a method.